This invention relates to a fuel injection system for an engine, and more particularly, to an improved charge forming system for an engine having vertically disposed cylinders.
It is well known that the induction and exhaust systems for multiple cylinder engines must be carefully designed so as to prevent adverse affects caused by the action of one cylinder on other and adjacent cylinders. This situation may be best understood by a reference to FIGS. 1 and 2, which show schematically induction and exhaust systems for three cylinder, in-line, two-cycle, crankcase compression internal combustion engines. In each instance, the engine has aligned cylinders A, B and C in which pistons are supported and which drive a crankshaft in a known manner. Each cylinder is provided with a respective induction system D, E and F which in the described constructions are independent from each other and comprises an inlet section in which a throttle valve G is positioned and a discharge section in which a reed-type check valve H is positioned so as to permit flow into the crankcase chambers of the cylinders A, B and C, respectively, but to preclude reverse flow. A suitable charge former is also employed which may supply fuel to the induction systems D, E and F, or which may supply fuel to either the crankcase chambers of the cylinders A, B and C, or incorporate direct injection for injecting the fuel directly into the combustion chambers. Because the induction systems D, E and F are separate from each other, the induction pulses from one cylinder will not be transmitted to or affect those of the other cylinders.
In the exhaust system, indicated by the reference character I in FIG. 1, there is provided a relatively long exhaust pipe J, K and L that extends from the exhaust ports of each cylinder A, B and C to a common atmospheric exhaust discharge M. With this type of arrangement, the exhaust pipes J, K and L can be made long enough so as to avoid any adverse affect from cylinder to cylinder. This is a preferred type of arrangement in most cases.
However, there are certain applications for internal combustion engines which do not permit this type of exhaust system. A specific example of such an application is an outboard motor. As is well known, outboard motors are extremely compact in nature and because of this they must D employ an exhaust system of the general type shown in FIG. 2 and which is indicated by the reference character N. In this exhaust system N, there is a common collector section O which receives exhaust gases from relatively short pipe sections P, Q and R. Also, it should be noted that this type of system generally employs a downwardly depending exhaust pipe S that extends into the drive shaft housing and lower unit for a discharge of the exhaust gases to the atmosphere. As a result of this, each exhaust port is disposed at a different distance from the discharge end and the exhaust pulses from one cylinder can reflect back and cause certain problems, particularly under extremely low speed, low load conditions, that can cause uneven running or other problems.
It has been found that these running problems can be eliminated or substantially reduced if the flow of fuel to the lowermost cylinder C is either discontinued completely or is reduced. Such an arrangement is disclosed in U.S. Pat. No. 5,387,163 That system has proven quite effective in reducing not only exhaust emissions, but improving running characteristics.
It has been found, however, that when the amount of fuel supplied to the lowermost cylinder is either stopped or substantially reduced, then there still may be some instances when running difficulties arise. This is because the engine must still generate the requisite amount of power in order to run smoothly, and it has been found that the effects between the respective exhaust passages can cause the remaining cylinders to run with an improper air-fuel ratio as a result of the exchange of exhaust pulses from one cylinder to the other.
It is, therefore, a principal object of this invention to provide an improved engine fuel supply system and method for operating an engine so as to improve running under low speed, low load conditions.
It is a further object of this invention to provide an improved arrangement for improving the running of an engine having two cylinders, one positioned vertically above the other and wherein either the induction or exhaust system from the cylinders communicate with each other at a relatively close point to the cylinders.
The foregoing discussion has been directed primarily at engines having exhaust systems that interconnect with each other quite close to their cylinders. The same problem, however, can arise when the intake systems communicate with each other close to the cylinders.
Therefore, it is a still further object of this invention to provide an improved method and apparatus for operating a multiple cylinder, vertically extending engine having either induction or exhaust systems which communicate with each other quite close to the cylinders.